Intravascular thrombosis is one of the most frequent pathological events accounting for greater than 50% of all deaths as well as a variety of other serious clinical problems. Factors which stimulate thrombosis include vascular damage, activation/stimulation of platelets, and activation of the coagulation cascade. Platelet activation and subsequent aggregation leads to the exposure of phospholipid on the platelet surface which facilitates the activation of coagulation factors X and II. Platelet activation and the resulting aggregation has been shown to be associated with various pathological conditions including cardiovascular and cerebrovascular thromboembolic disorders such as unstable angina, myocardial infarction, transient ischemic attack, and stroke.
When a blood vessel is injured, either acutely or chronically, for example, by clinical interventions or pathophysiological processes, such as atherosclerosis, platelets and leukocytes may be activated and may adhere to the injured blood vessel surface, as well as to each other in a homotypic and heterotypic fashion. Such activation, primary adhesion, and secondary homotypic and heterotypic cellular aggregation, involving cell-associated and soluble adhesion proteins (also referred to as adhesive proteins), including fibrinogen, leads to occlusive thrombus formation in the lumen of the blood vessel. The family of receptor proteins which recognize and bind adhesion proteins are referred to as integrins.
During endothelium injury, the basement membrane zones of blood vessels express several adhesion proteins, including von Willebrand factor, fibronectin, and fibrin. Additionally, several members of the integrin family of adhesion protein receptors are expressed on the surface of endothelial, smooth muscle and on other circulating cells.
Among these integrins is .alpha..sub.v /.beta..sub.3, the endothelial cell, fibroblast, and smooth muscle cell receptor for adhesion proteins including von Willebrand factor, fibrinogen (fibrin), vitronectin, thrombospondin, and osteopontin.
It has been reported that the integrin .alpha..sub.v /.beta..sub.3 is expressed on blood vessels in granulation tissue and that enhanced expression of .alpha..sub.v /.beta..sub.3 in human blood vessels occurs during angiogenesis (Brooks et al. Science 1994, 264: 569-571). Anti-.alpha..sub.v /.beta..sub.3 antibody was reported to block bFGF-induced angiogenesis, suggesting a potential role of .alpha..sub.v /.beta..sub.3 in angiogenesis. Additionally, .alpha..sub.v /.beta..sub.3 has been implicated in tumor progression and neovascularlization (Brooks et al. Science 1994, 264 5158: 569-571).
Monoclonal antibody, LM609 (produced by hybridoma LM609 ATCC HB 9537), disclosed in PCT Application Publication No. WO 89/05155 (published Jun. 15, 1989) and Cheresh et al., J. Biol. Chem. 1987, 262:17703-17711 binds to .alpha..sub.v /.beta..sub.3 complex. PCT Application Publication No. WO 93/20229 discloses monoclonal antibodies, which bind to the .alpha..sub.v /.beta..sub.3 receptor expressed on the surface of osteoclasts. Monoclonal antibody 23C6, which binds to .alpha..sub.v /.beta..sub.3 was reported to be able to disrupt osteoclast function (Horton et al., Cancer Res., 1985, 45:5663-5669; Horton et al., Exp. Cell. Res., 1991, 195:368-375). Monoclonal antibody 13C2 (Horton et al., Cancer Res., 1985, 45:5663-5669) was shown to bind the .alpha..sub.v portion of the .alpha..sub.v /.beta..sub.3 molecule, whereas several other monoclonal antibodies were reported to recognize the .beta..sub.3 portion (Nesbitt et al., in "Leukocyte Typing IV, White Cell Differentiation Antigens", Knapp et al. (eds.) 1991, p. 1037). The specific monoclonal antibodies variously reported in the art were shown to also bind to endothelial cells and various melanoma cell lines.
It is well known that platelet activation and aggregation are implicated in various thromboembolic disorders. Platelet aggregation is known to involve the binding of fibrinogen to the activated membrane surface integrin, the fibrinogen receptor GPIIb/IIIa. Inhibition of platelet aggregation by inhibition of GPIIb/IIIa to fibrinogen is, therefore, recognized as an attractive target for antithrombotic therapeutic intervention. A variety of GPIIb/IIIa antagonists are presently in clinical development for the treatment of thrombosis.
Similarly, inhibitors of thrombin have been demonstrated to have antithrombotic efficacy in various arterial and venous thrombosis models.
However, it is recognized that the inhibition of platelet aggregation or thrombin may result in a hemostatic imbalance with consequent bleeding time prolongation and in clinical situations bleeding complications and bleeding risk may arise (Simoons et al., Circulation 1994, 89:596-603; Cannegieter et al., Circulation 1994, 89: 635-641; FDC Reports: Pink Sheet, Vol. 56, 1994). Increased bleeding risk has been associated with both GPIIb/IIIa antagonist and thrombin inhibitor antithrombotic therapies (The Guesto IIa Investigators, U.S., Canada, Europe, Australia and New Zealand, Circulation 1994, 40 (I-231): 1240; Lefkovits et al., Circulation 1994, 40 (I-231): 3037; Tcheng et al., Circulation 1994, 90: 1757-1764; Antman et al., Circulation 1994; 90: 1624-1630). Furthermore in the case of direct or indirect thrombin inhibitors, a rebound activation of the coagulation system has been demonstrated upon the discontinuation of these therapies (Theroux al., N. Engl. J. Med. 1992, 327:141-145; Gold et al., J. Am. Coll. Cardiol. 1993, 21:1039-1047).
In view of the inherent limitations of the presently available GPIIb/IIIa antagonist and thrombin inhibitor approaches for antithrombotic therapy, there is a need for new therapeutic targets for the treatment and prevention of thrombosis which are more effective and safer than present antithrombotic therapeutic approaches. An ideal antithrombotic strategy would prevent arterial and venous thrombotic disorders, without significantly affecting the hemostatic balance, that is, without significantly affecting platelet aggregation functions or the blood coagulation parameters. The present invention provides new methods for the treatment (including prevention) of thrombosis which do not significantly alter hemostatic balance and do not significantly inhibit platelet aggregation and do not significantly inhibit coagulation. A preferred aspect of the present invention comprises methods of treatment (including prevention) of thrombosis and/or thromboembolic disorders comprising administering to a subject in need of such treatment an agent that selectively inhibits the binding of vitronectin to the .alpha..sub.v /.beta..sub.3 receptor.
None of the above references teach or suggest the use of an .alpha..sub.v .beta..sub.3 receptor selective ligand to prevent thrombus formation.